A typical gasifier includes a combustion zone for fuel (e.g., pellets) and a grate supporting the fuel bed during combustion. Ash falls through the grate and is collected in some fashion. When the fuel is of a predetermined composition, the grate can be very simple in design, e.g., a plate with holes or slots in it. Those skilled in the art have also devised rotating grates and grates which shake in order to encourage the ash to fall through the grate. See “State of the Art for Small Scale Gas Producer-Engine Systems” by Ali Kaupp first published by the German Appropriate Technology Exchange and reissued by the Biomass Energy Foundation Press, Golden, Colo. 80401 incorporated herein by this reference.
The applicant's co-pending application U.S. patent application Ser. No. 12/070,032 filed Feb. 14, 2008 discloses a new waste-to-energy method wherein feedstock waste is shredded, dried, and pelletized. The pellets are then combusted in a gasifier to produce a gas used to operate a generator which generates electricity. In such a waste-to-energy system, the composition of the fuel converted in the gasifier can vary widely. The feedstock waste, for example, may contain metal, ceramic, and/or other waste material which are not combustible in this process.
Such non-fuel products collect on the gasifier grate and impede the flow of gas through the gasifier. If the pressure drop along the reactor increases significantly, the result can be a dangerous “updraft” condition. In any case, the efficient operation of the gasifier depends on the correct pressure drop along the reactor.
Known shaking or other grates are ineffective at removing the non-fuel “clinkers” which collect on the grates. And, making the grate openings larger in size so that the clinkers pass through the grate considerably reduces yield because it allows for large, not fully converted feedstock to pass through. This defeats the purpose of the grate. Manually cleaning the grates of clinkers is inefficient as well since the gasifier must be shut down in order to do so. During the shut down period, no producer gas is produced.